Deposition of thin films is one of the key processes in semiconductor manufacturing. A typical wafer goes through deposition of several thin films, some of which may completely or partially remain in the final electronic device, while others may only temporarily remain on the wafer and serve some intermediate processing needs. For example, an ashable hard mask film may be used as an etch hardmask layer. Such film is first deposited on a wafer and then partially removed to define circuit line patterns. An etchant is then applied to remove some of the underlying dielectric forming trenches and vias for the future circuit lines. Eventually, all remaining ashable hard mask film is removed from the wafer.
Various deposition processes are used to deposit thin films. For example, an ashable hard mask film may be deposited using chemical vapor deposition (CVD), or more specifically plasma enhanced chemical vapor deposition (PECVD), processes. One consequence of almost any deposition process is that the film material is not only deposited onto the wafer but also on the interior surfaces of the deposition chambers, thereby forming residues. These residues can build up over time and dissolve, detach or otherwise disperse through the deposition chamber causing contamination. The built-up residues are periodically removed to avoid such contamination.